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| author | Peter Zijlstra <peterz@infradead.org> | 2015-08-20 10:34:59 +0930 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2015-11-09 10:12:59 -0800 |
| commit | 631778f7c2b8d68f20197f3533db7e37ad518561 (patch) | |
| tree | 1b236e74f05ea1148e12f46602c662efbad4d8ea /kernel | |
| parent | c69cba6c93d95bb70ea7914f47e520aa99022a27 (diff) | |
module: Fix locking in symbol_put_addr()
commit 275d7d44d802ef271a42dc87ac091a495ba72fc5 upstream.
Poma (on the way to another bug) reported an assertion triggering:
[<ffffffff81150529>] module_assert_mutex_or_preempt+0x49/0x90
[<ffffffff81150822>] __module_address+0x32/0x150
[<ffffffff81150956>] __module_text_address+0x16/0x70
[<ffffffff81150f19>] symbol_put_addr+0x29/0x40
[<ffffffffa04b77ad>] dvb_frontend_detach+0x7d/0x90 [dvb_core]
Laura Abbott <labbott@redhat.com> produced a patch which lead us to
inspect symbol_put_addr(). This function has a comment claiming it
doesn't need to disable preemption around the module lookup
because it holds a reference to the module it wants to find, which
therefore cannot go away.
This is wrong (and a false optimization too, preempt_disable() is really
rather cheap, and I doubt any of this is on uber critical paths,
otherwise it would've retained a pointer to the actual module anyway and
avoided the second lookup).
While its true that the module cannot go away while we hold a reference
on it, the data structure we do the lookup in very much _CAN_ change
while we do the lookup. Therefore fix the comment and add the
required preempt_disable().
Reported-by: poma <pomidorabelisima@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Fixes: a6e6abd575fc ("module: remove module_text_address()")
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/module.c | 8 |
1 files changed, 6 insertions, 2 deletions
diff --git a/kernel/module.c b/kernel/module.c index 61fb677211cb..fd2afdf48a89 100644 --- a/kernel/module.c +++ b/kernel/module.c @@ -942,11 +942,15 @@ void symbol_put_addr(void *addr) if (core_kernel_text(a)) return; - /* module_text_address is safe here: we're supposed to have reference - * to module from symbol_get, so it can't go away. */ + /* + * Even though we hold a reference on the module; we still need to + * disable preemption in order to safely traverse the data structure. + */ + preempt_disable(); modaddr = __module_text_address(a); BUG_ON(!modaddr); module_put(modaddr); + preempt_enable(); } EXPORT_SYMBOL_GPL(symbol_put_addr); |